Debye model

About: Debye model is a research topic. Over the lifetime, 7462 publications have been published within this topic receiving 133987 citations.

First-Principles Study of Lattice Dynamics and Thermodynamics of TiO2 Polymorphs

Abstract: The structural, phonon, and thermodynamic properties of six TiO2 polymorphs, i.e., rutile, anatase, columbite, baddeleyite, orthorhombic I, and cotunnite, have been systematically investigated by density functional theory. The predicted volumes, bulk modulus, and Debye temperature are in good agreement with experiments. The phonon dispersions of the TiO2 polymorphs were studied by the supercell approach, whereas the long-range dipole–dipole interactions were calculated by linear response theory to reproduce the LO–TO splitting, making accurate prediction of phonon frequencies for the polar material TiO2. The calculated phonon dispersions show that all TiO2 polymorphs are dynamically stable at ambient pressure, indicating the high-pressure phases might be quenched to ambient conditions as ultrahard materials. Furthermore, the finite temperature thermodynamic properties of TiO2 polymorphs were predicted accurately from the obtained phonon density of states, which is critical in the future study of the press...

Thermodynamic properties of ferromagnesium silicate perovskites from vibrational spectroscopy

Abstract: Infrared (IR) reflectance and absorbance spectra obtained from polycrystalline and single-crystal perovskites of MgSiO3 and (Mg0.9Fe0.1)SiO3 compositions yielded virtually all the expected fundamental modes. Near-IR absorbance spectra indicate that the polycrystals were anhydrous, whereas the single crystal contained about 0.06 wt % H2O. A Kieffer-type model was used to calculate heat capacity, entropy, and Debye temperature for the orthorhombic perovskite phase. The calculated values at 298 K are Cp = 82 ± 2 J/mol K and S = 56 ± 2 J/mol K. Our calculated Cp agrees with calorimetric data within 5%. Above 500 K, the Debye temperature is nearly constant and equals 960±30 K. The bulk modulus is calculated from vibrational frequencies to be 265±13 GPa which lies within 2% of recent experiments. The Clapeyron slope for the phase transition between ilmenite and orthorhombic perovskite is calculated to be 1.110.6 MPa/K which is close to the experimental determination.

Elastic moduli of niobium carbide and tantalum carbide at high temperature

Abstract: The Young's, shear and bulk moduli of polycrystalline NbC 0.95 and TaC 0.99 were determined from room temperature to 1500°K by the sonic resonance technique. The Young's and shear moduli decrease linearly with increasing porosity, and also decrease with increasing temperature, in agreement with the Wachtman's empirical equation. The bulk modulus decreases with increasing porosity and with increasing temperature. The Gruneisen constant and Debye temperature of both carbides were determined. The Poisson ratio increases with increasing temperature.

Lattice Vibrations in Alkali Halide Crystals. I. Lithium and Sodium Halides

Abstract: Vibrational frequency distributions for the lithium and sodium halides have been evaluated on the basis of the Born lattice theory by the use of Blackman's numerical‐sampling technique. Both room temperature and extrapolated 0°K parameters have been used in the calculation. Specific heats, the corresponding Debye characteristic temperatures, and the moments of the distributions have been evaluated directly from the frequencies. Comparison is made with experimental data and with other theoretical work.